An explosion at a warehouse in the port of Beirut, Lebanon, killed more than 70 people and left more than 4,000 people injured on Tuesday. As a result of the explosion, videos uploaded to social media show lots of maroon smoke and the apocalyptic extent of the destruction, with buildings planned miles. According to a report by Al Jazeera, Lebanese Prime Minister Hassan Diab said the explosion was driven by a warehouse containing more than 2,700 tonnes of ammonium nitrate, confiscated and stored for about six years in the port.
The explosive potential of ammonium nitrate is well understood and has been used in many terrorist attacks including the bombing of Oklahoma City in 1995. So what is ammonium nitrate, why is it explosive and why do we use it?
Ammonium nitrate is a chemical compound that contains the element nitrogen (as well as hydrogen and oxygen) and is commonly used in agriculture as a fertilizer. Plants rely on photosynthesis and convert sunlight into energy with chlorophyll. Nitrogen is an important element in this process and ammonium nitrate is particularly good compared to other fertilizers when it comes to supplying plant nutrients.
It is also an explosive compound and is used around the world for mining and construction operations that require detonations. Under normal conditions, the chemical is very stable. It can explode after exposure to pollutants or fuel oil and then heat up, triggering a cascade of reactions.
When heated to over 170 degrees Fahrenheit, ammonium nitrate begins to decompose. But with rapid heating or detonation, a chemical reaction can occur that converts ammonium nitrate to nitrogen and oxygen and water vapor. The products of the reaction are harmless – they are in our atmosphere – but the process releases enormous amounts of energy.
“The idea of making some kind of explosive is to go from a high-energy association to a low-energy one,” explains Ian Rae, a professor at the University of Melbourne. “The energy released is what you get as explosive power.”
This also requires pressure to build up in a cramped space without being able to spread. Burning ammonium nitrate in an open field, for example, is unlikely to lead to an explosion, Rae said.
In addition, not all ammonium nitrate is used in the explosion and exploded. Some of it decomposes slowly and creates toxic gases such as nitrogen oxides. It is these gases that are responsible for the reddish-brown smoke smoke that is seen as a result of the Beirut explosion, Rae said.
Once the fireball has appeared in the video above, you can immediately see the shock wave expanding away from the explosion. Moisture in the air condenses quickly and forms a white sphere around the explosion zone. It is not clear what else may have ignited or exploded in the blast – or what was stored at the bridges – but Prime Minister Diab is expected to make this information known “soon”, according to The Guardian.
Due to the explosive potential of ammonium nitrate, countries and trade unions set strict rules for how they are to be stored and processed. “It is usually kept under controlled conditions and modified volumes to minimize the risk of explosion,” said Brent Kaiser, a plant biologist at the University of Sydney. In Australia, the storage and use of ammonium nitrate is monitored to prevent these types of explosions from occurring, Kaiser said.
The US Environmental Protection Agency, in collaboration with the Swedish Work Environment Authority and the Agency for Alcohol, Tobacco, Firearms and Explosives, lists a number of statutes and regulations involved in the manufacture, processing and storage of ammonium nitrate. Facilities that contain large amounts of chemicals are being investigated by the Department of Homeland Security. The US Office of Cybersecurity and Infrastructure has also proposed a program to carefully regulate the sale of ammonium nitrate transfer.
Accidental detonation of ammonium nitrate has resulted in a number of accidents during the last century. In 2015, explosions caused in part by the detonation of about 800 tons of ammonium nitrate robbed the Pian Harbor in Tianjin and killed 173 people.
An explosion of ammonium nitrate was responsible for the worst industrial accident in US history in 1947. A ship in the port of Texas City, Texas, carrying about 2,300 tons of ammonium nitrate fired, probably through a discarded cigarette, causing a series of explosions that killed 581 people.
Two explosions are said to have rocked in the harbor. Although the causative agent of the larger, second explosion appears to be ammonium nitrate, the full extent of the devastation in Lebanon is not yet fully understood and an investigation will be conducted. “What happened today will not happen without responsibility,” Diab said. He has also announced that Wednesday will be a national day of mourning in the country and the port and the surrounding region have been declared a disaster zone.
“This is clearly a very significant explosion, and the reported number of deaths is likely to be much higher than currently identified,” said David Caldicott, a senior clinical lecturer in medicine at the Australian National University.